The agreement jointly reached by American Conference of Governmental Industrial Hygienists (ACGIH), International Standards Organization (ISO) and Comite Europeen de Normalisation (CEN) is generally accepted as a new standard for the health-related aerosol size-selective sampling. The agreement includes a new definition of a respirable aerosol, which is in fact a compromise between the two definitions given by British Medical Research Council (BMRC) and American Conference of Governmental Industrial Hygienists (ACGIH). As far as 50% cut-off diameter is concerned, it is set respectively by BMRC and ACGIH (1985) as 5 .mu.m and 3.5 .mu.m, with the newest one being 4 .mu.m set by ISO/CEN/ACGIH. As far as the slope of the penetration curve, the newest definition is milder than the two old definitions.
The 10 mm nylon cyclone and the SKC cyclone are most commonly used in Taiwan for sampling the respirable particles. According to the research report [Bartley et al., Am. Ind. Hyg. Assoc. J., 55(11): 1034-1046, 1994], these two cyclone samplers can conform to the standard set forth by ACGIH/ISO/CEN by means of an appropriate flow-rate adjustment. However, the inclinations of their penetration curves are steeper than the inclination of the international newest convention curve. For this reason, there will be an underestimation and an overestimation with regard to the greater and the smaller particles at the time when the sampling is actually carried out. There was a research report to the effect that the overestimation and the underestimation can cancel out each other, and that the sampling error may not be too great. However, under the circumstance that the aerosol distribution is extreme, the sampling error may be rather considerably serious. In light of this, Gautam and Sreenath derived an improved multi-inlet cyclone from a 10 mm nylon cyclone in 1997. According to the test results, its penetration curve has a slope and 50% cut-off diameter, which are more closer to those of the convention curve. In addition, the errors resulting from the sampling direction is reduced.
The design of the cyclone sampler is based on the vortex as well as the principle of inertia impact. The particles are likely to deposit, trip, slide and even roll at the moment when the particles are thrown by the centrifugal force to make contact with the tube wall, depending on the characteristics of the particles and the tube wall. This implies that the separation efficiency curve of the particles may deviate due to the load of particles. With regard to the problem of dust load in the cyclone, it was found by Blachmann and Lippman that the solid particles were gradually deposited on the inner wall opposite to the inlet of the 10 mm nylon cyclone. Please refer to Blachman, M. W. and Lippman, M., Am. Ind. Hyg. Assoc. J., 35: 311-326, 1974. As a result of the particle deposition, the effective radius of the cyclone is reduced, thereby resulting in an improvement on the particle collecting efficiency. As the particles are accumulated to have a considerable thickness, an avalanche is likely to take place to result in an increase in the effective radius of the cyclone once again. As a result, the particle-collecting efficiency is once again lowered. However, they neither quantify the problem nor propose solutions to the problem. In order to cope with the problem as described above, a new BB cyclone was disclosed. The BB cyclone is made of an aluminum alloy material conductive to electricity, and has a greater inner diameter and an exit tube length for reducing the particle deposition on the inner wall as well as the impact of the particle load on the collection efficiency. However, the BB cyclone is similar in pattern and principle to the conventional cyclone such that the particle deposition also takes place in the BB cyclone, and that the effective radius of the BB cyclone is decreased, and further that the separation efficiency curve of the BB cyclone is affected by the particle load.
The aerosol that is inhaled through the respiratory duct may be deposited in the body tissue due to the action of various depository mechanisms, such as gravity sinking, diffusion, static, impact and interception. Moreover, the inhaled aerosol may be exhaled. The aerosol deposited in the respiratory duct can not be easily removed and may be responsible for various disorders of the respiratory system. The removal rate of the aerosol that is deposited in the respiratory system varies from one part to another of the respiratory system. For this reason, the amount of aerosol deposit and the body part in which the aerosol is deposited are two important factors that must be taken into consideration in terms of the relationship between the health and the aerosol. The conventional method for sampling aerosol at the work site is based on the total aerosol and is therefore insufficient to meet the actual requirements of the investigation.
For the convenience of investigating the health relationship between the aerosol and the human body, the human respiratory system may be divided into three groups, which include head (mouth, throat, nostrils, etc.), bronchus (trachea, or windpipe), and lung (pulmonary alveolus, pleura).
The aerosol with a greater diameter is often intercepted and deposited in the nose. The aerosol deposited in head and bronchus may be removed by means of flagellation. The aerosol with a smaller diameter is prone to deposit in the pulmonary vesicle and can be removed therefrom only by phagocyte. The ingestion of aerosol by the phagocyte is less efficient than the removal of aerosol by the flagellation. In light of the reasons stated above, it is necessary to develop the so-called "size-selective sampler" for measuring the concentration of the aerosol that is deposited in a specific portion of the respiratory system. The size-selective sampler is based on the ideal size-selective standard in which the aerodynamic diameter of aerosol is used as a function.
In the past ten years, the use of the aerosol size-selective sampler involved the respirable standard suggested by BMRC (British Medical Research Council). However, ISOC (International organization for standardization) suggested in 1985 the evaluation standards which include the inhalable standard, the thoracic standard, and the alveolar standard. In the same year, ACGIH came up with the standards which were basically similar to ISOC's standards. In other words, there are so many standards that were suggested by various organizations. None of these standards is internationally accepted.
Three fractions of size-selective sampling suggested by Sidney C. Soderholm in 1989 are currently accepted by ACGIH, ISO, CEN (Commite Europeen de Normalisation) and NIOSH. For more details, plese refer to Soderholm S. C., Ann. Occup. Hyp. 33 (3), 303-320, 1989. The three size-selective sampling methods are described hereinafter.
1. Inspirable or inhalable fraction
The size-selective sampling efficiency curve of the inspirable or inhalable fraction is a continuation of the standard suggested by ACGIH in 1985.
Inhalable fraction: EQU SI(d)=50%*(1+e.sup.-0.06d) (1)
0&lt;d&lt;=100 .mu.m PA1 SI(d): collection efficiency of inhalable fraction sampler at the time when aerodynamic diameter is d .mu.m. PA1 X={ln(d/.GAMMA.)}/{ln(.SIGMA.)} PA1 .GAMMA.=11.64 .mu.m PA1 .SIGMA.=1.5 PA1 ST: sampling efficiency of the thoracic fraction sampler PA1 F(x)=cumulative probability function of the standardized variable x ##EQU1## PA1 F(X) is the same as above PA1 .GAMMA.=4.25 .mu.m PA1 .SIGMA.=1.5
This is based on the disclosure by Vincent & Armbruster in 1981, who compiled the data of the research in which the inhaling of aerosol through mouth and nose of the human head model was studied in the wind hole. The international standards adopt the concept of inhalable aerosol and add this fraction for the possibility of aerosol deposition in mouth, throat, and nostrils.
2. Thoracic fraction
According to Yu et al., 1981; Miller et al., 1988; Heyder et al., 1986; Rudolf et al., 1988 (Heyder, J. et al., J. Aerosol Sci., 17: 811-825, 1986 and Rudolf, G., J. Aerosol Med., 1:209-210, 1988), the data can be inferred on the basis of the theory that the fraction is deposited in the respiratory duct by taking the actual sampling efficiency into consideration. As a result, the thoracic fraction was defined as follows:
Thoracic fraction: EQU ST(d)=SI(d)*{1-F(x)} (2)
The numerical method for computing he value of F(x) is as follows: ##EQU2## EQU G(y)=0.5(1+0.14112821y+0.08864027y.sup.2 +0.02743349y.sup.3 -0.0039446y.sup.4 +0.00328975y.sup.5).sup.-8 (5)
When -4&lt;Y&lt;4, the absolute error is smaller than .+-.0.0001.
3. Respirable fraction
According to Milleret et al., 1988; Heyder et al., 1986 (Please refer to the references cited above); Lippmann & Albert, 1969; Chan & Lippmann, 1980; and Heyder et al., 1986, the studies were done on the aerosol deposit in the bronchus and the alveolus. They also took the actual sampling efficiency of the sampler into consideration when they defined the standard.
Respirable fraction: EQU SR(d)=SI(d)*{1-F(x)} (6)
The conventional size-selective sampler is based on the principle of the aerosol inertia. The aerosol of a large diameter and the aerosol of a small diameter are separated by an impact device or a cyclone.